If you call her, and she doesn't come to you..... Go get her and make her come to you.
Let her drag a leash or long-line... something you can step on or catch that way you don't have to chase her around.

Pet her up when you bring her back to the point you called her from, give her a cookie, and let her go back to playing.

Call her again, go get her, cookie, pets, turn her loose.

The key is don't give a command you don't intend to enforce, don't be lazy, don't call her and call her and call her..... and then throw your hands up in the air and blame the dog. This is a human problem, it's training.

Spend the time on this now and you won't regret it down the road.
Dogs are not born trained, it's your responsibility to teach her.
Good luck
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I probably think a little different on this...so take it for what its worth.

A 5 month old pup is a live "gangl" of nerves...every input leads to a response...and overload is reached very easily. Don't run the pup with other dogs and expect obedience right now.

Run the dog alone for now. Teach the dog "come around" to the whistle... be careful that you don't have the dog come all the way into you. "Come around" and "come" are two different commands. Toot the whistle twice, and let the dog see you walking in a different direction....this means when the dog looks up, it should see you from the side, either your left or right shoulder is facing the dog...because you are headed in a new direction. Now overlay either a collar with a pager or a tone on top of the come around whistle command (I prefer the Dogtra collars with pager). Toot the whistle twice and at the same time hold down the pager until the dog turns towards you...then release the pager. The dog will do this well if you have done the basics. If the dog does not respond to the pager and the whistle, it is time to use the continuous stimulation. PLEASE understand what I am saying....DO NOT shock the dog so as to cause it to scream....find a level on the collar that causes discomfort no pain (each dog has a different level). It goes something like this...Toot twice and hit the pager.....the dog does not turn towards you(and it has been conditioned to know what this means)...immediately hit the continuous stimulation BUT release when the dog has turned towards you. You are teaching the dog that it can turn off the discomfort (eventually avoid it) by turning and coming towards you on the whistle and the pager. DO NOT yell, scream, scold when the dog does something wrong...let the dog learn to reward itself.

Once this has been learned, you are ready to enforce the come around command in the presence of stimulus like another dog...or the cow in the next pasture!! IMPORTANT....never use a collar in any situation where the dog might think that another dog is responsible for the electrical stimulation. Toot the whistle and hit the pager when the dog is separated from its bracemate and apply the same procedure if the dog does not come around.

One caveat.....pick your battles.....don't go out in a day and expect to get all of this done. Do it slowly by steps. Do this too much and too often and you can limit a dog's independence. In addition, once your young dog has been on game, it will most likely be less interested in other dogs in the field.

I have a nine month old male....and using this method he is 90% reliable on the come around command. I don't use it much though....I want to see him reach out more ...so I tend to let him go right now.

The reason I like this method is that after dogs are trained with the pager, I can hunt totally silently in the field. I hit the pager to have the dog come around if needed without any whistle and only my dog "hears" the signal.
Later on I combine it with hand signals....in the water, this is very useful.